Demands for high-speed and high-capacity auxiliary storage devices are increasing. Especially, in a large-scale computer, many configurations are used, in which a storage (a disk array) assembled by storage devices is connected with SAN (Storage Area Network; a memory area network).
Among SANs, an SAN employing an iSCSI (Internet Small Computer System Interface) is attracting attention as a developing market, since a device cost is relatively low and existing infrastructures can be effectively utilized.
For example, a technology about SAN using the iSCSI is disclosed in Japanese Laid Open Patent Application (JP 2005-151437 (patent literature 1). In a system described in patent literature 1, information indicating that an SCSI command is encapsulated is stored in a header of a TCP (Transmission Control Protocol) packet, and whether the SCSI command is encapsulated or not can be judged without extracting the SCSI command, by reference to this information.
Since the iSCSI uses a TCP/IP technology at a layer below the SCSI protocol, the inventor expects that flow control with a high adaptation (flexibility) is attained by applying an open flow protocol to a system employing the iSCSI.
The open flow protocol is a method of controlling a route by a unit flow, and suggested by OpenFlow Consortium (refer to non-patent literature 1). In the open flow protocol, a series of communications from one point to another point are defined as “a flow”, which is determined by a combination of a MAC address, an IP address, and a port number or the like. When the open flow protocol is employed, the route can be changed for each of flows, instead of uniformly being determined based on information about a source and a destination. Moreover, the route is controlled end to end, not only between adjacent devices.
However, currently, in the OSI Reference Model, a switch (hereinafter, referred to as an open flow switch) is able to treat only layers from the layer 1 to the TCP layer of the layer 4, and is not able to treat the iSCSI layer which is above those layers. Though the iSCSI layer is within the layer 4 in the OSI Reference Model, since the iSCSI layer is above the TCP layer, the open flow switch is not able to recognize it. Accordingly, current open flow system cannot carry out flow control using an SCSI name (an initiator name or a target name) of the iSCSI layer.
In order to carry out a flow control more flexibly, the open flow switch is preferably able to treat information about the iSCSI layer. Especially, if the open flow switch is able to treat the iSCSI name, usefulness is increased because the flow control is carried out based on the iSCSI name. On the other hand, if the flow control using the iSCSI name is not possible, since the flow is not controlled for each of initiators or targets, it is difficult to construct a network having large adaptation and effectively use a logical disk in the SAN.
On the other hand, for example, technologies about flow control which uses the TCP are described in Japanese Laid Open Patent Application JP 2006-129487 (refer to patent literature 2) and Japanese Laid Open Patent Application (JP-Heisei 11-239163 (refer to patent literature 3). In patent literature 2, a system is described, which uses an option field of a TCP packet to distinguish a terminal which is connected to a server. Moreover, in patent literature 3, a technology is described in which a switch carries out flow control between LANs.